A technology for producing synthesis gas from crude gas from various gasification processes for solid or liquid fuels. To limit the temperatures in a subsequent strongly exothermic CO shift reaction to adjust the H2/CO ratio, the crude gas which has been freed of dust flows through two shift reactors arranged in series. The first reactor has a specific reaction-kinetically limited catalyst and the second reactor has a conventional sour gas catalyst. The specific catalyst used in the first reactor limits the exothermic shift reaction to such an extent that the reaction temperatures in the first and second reactors remain so low to avoid thermal damage to the catalysts even without introduction of external steam, and the desired gas composition is achieved.